1. Field of the Invention
The present invention relates to an image processing system, an image processing method, and a computer program product for performing a predetermined image processing with respect to an image signal.
2. Description of the Related Art
A space variant process for the image processing has been employed to perform the different image processing for each local region.
U.S. Pat. No. 3,465,226 discloses the technology where an image signal is divided into a plurality of regions based on the texture information to obtain the gradation conversion curve based on the histogram for each region such that the weighting interpolation is executed based on the distance between the respective regions. This makes it possible to enable both the space variant gradation process and the maintenance of the continuity between the regions to obtain the high-definition image signal while preventing the crash in the tone with respect to the image in the wide dynamic range.
For example, U.S. Pat. No. 3,402,630 discloses the technology for performing the contrast enhancement by correcting the high frequency component based on the low frequency component derived from the multiresolution decomposition and the odd variable function. This makes it possible to allow the processing which combines the space variant contrast enhancement with maintenance of the continuity between the regions so as to provide the high-definition image signal for improving the diagnostic performance with respect to the medical image.
Japanese Unexamined Patent Application Publication No. 2004-72422 discloses the technology for performing the noise reducing processing which is different for each pixel by estimating the noise amount for each pixel based on the noise model. This makes it possible to perform the space variant noise reducing process, thus providing the high-definition image signal while minimizing the degradation of the edge component.
In U.S. Pat. No. 3,465,226, the weighting interpolation is inevitable for each pixel for the purpose of maintaining the continuity between the regions, which may demand more calculation work and longer processing time. When the disclosed technology expected to be used for the luminance signal is applied to the color image signal, such problem as having the color signal departing from the color reproduction region may occur.
In U.S. Pat. No. 3,402,630, the high frequency component is corrected based on the odd variable function. However, as the process for automatically setting the odd variable function is not specified, it should be defined in the subjective assessment manner. Though the technology may be applicable to the medical image under the limited shooting condition, the appropriate contrast enhancement cannot be performed automatically with respect to the various types of subject.
In Japanese Unexamined Patent Application Publication No. 2004-72422, the noise reducing process is performed separately from the other gradation correction process and the edge enhancement process, which may fail to appropriately perform the respective processes in a mutually appropriate manner.
It is an object of the present invention to provide an image processing system, an image processing method, and a computer program product which enable the high speed correction process with respect to the image signal while allowing both the space variant process and maintenance of the continuity among the local regions.